I got an MS in Zoology, so it's a favorite subject of mine, but I have a hard time sharing my interest with my kids (besides catching bugs, having lots of pets over the years and reading National Geographic...) This year, on some recommendations from a couple of people here, I got Real Science Odyssey for Life Science. I have really liked it, and the kids have, too. So far we have done some good observational activities (outside doing a plot study and studying the parts of an egg) and some fun models (jello models of plant and animal cells and this week a karo syrup based model of blood). I love that the lessons are one page of text. I feel like it hits the key points of the material, plus gives a good explanation, but keeps it short enough so the kids stay interested. We've been supplementing with relevant Bill Nye videos and the Discovery Ed streaming stuff (the kids dig Slim Goodbody) and I feel like it's a really good curriculum for my kids.
Anyways, just wanted to share as I've seen lots of science threads pop up lately. You can download a pretty good sample at their website. I'd looked at the sample before, but it didn't win me over. Really doing it, though, has made me a fan.